"Soil release" herein is produced when fabrics, especially fabrics having a synthetic fiber component, are laundered in an aqueous bath in a domestic or institutional setting wherein the aqueous bath comprises at least one surfactant and a certain specific kind of oligomeric ester, typically at low levels such as five to a few tens of parts per million.
Soil release is especially pronounced on polyester fabrics. It is quite distinct from the usual cleaning effect of laundry detergent surfactants and builders, especially in that one or both of the following occur: (a) marked improvement in the release of oily soils from soiled fabrics over that which would be obtained using a surfactants and/or builder alone; and (b) multiwash effect, e.g., fabrics repetitively laundered tending to be cleaned progressively more easily over two, three or four wash-wear cycles.
Soil release in an aqueous laundry context is rather different from industrial finishing of yarns and fibers, warp-sizing and the like in terms of the general kinds of s.r.a. compositions which work best. This may be a consequence of some substantial differences in the process conditions. In any event, laundry s.r.a.'s of the type herein are typically applied to fabrics in washing-machines, with appreciable concentrations of soil as well as aqueous surfactant and builder present. The s.r.a. typically deposits to only a limited extent on the fabrics. In contrast, industrial finishing is commonly done in highly controllable process equipment, such as padders. Typically the textile is clean, and the concentration of cleaning agents (if any) tends to be low, at least at the stage at which it is desired to exhaust a soil release treatment onto a textile substrate.
Just as there are technical differences between laundering and industrial finishing, so too are there discernible differences between laundry detergent formula types such as granular, liquid, gel, paste-form, and dryer-added types of laundry detergent formulae. Formulators in the detergent arts are acutely aware of the problem that various forms of detergent compositions have their own built-in formulation constraints. For example, solid-formulated detergents need ingredients generally capable of dispersing or dissolving in aqueous laundry baths, while liquid formulae commonly need ingredients which are freely mixable without excessive chemical or physical interaction such as phase changes or precipitation.
In addition to differences between detergent formula types capable of affecting choice of soil release agent, it is part of the discovery leading to the present invention that soil release agents are not all equal in terms of their ability to function satisfactorily in the presence of anionic detergent surfactants. Indeed, anionic detergent surfactants tend to inhibit the function of soil release agents.
Whereas the foregoing background describes some of the principal ways in which laundry soil release agents are thought to work and points to some of the differences between laundry and industrial s.r.a. applications, it is not intended to limit "soil release" or "s.r.a." as applied herein to any particular theory of operation: it is fully in accordance with the present invention that under appropriate conditions of s.r.a. use as further described hereinafter, benefits over those mentioned hereinabove, even quite different from them, may also be obtained.
In general, materials capable of the above-outlined laundry "soil release" and which do not have as their primary function surfactancy, detergent building, industrial durable finishing or the like are termed "soil release agents" (s.r.a.) herein.
Set against this technical backdrop, the instant invention has to do with improving laundry-type s.r.a.'s, especially in light of the above-identified need for improved s.r.a.'s for working in the presence of granular laundry detergents containing anionic detergent surfactants. Moreover, the invention is specifically concerned with chemically modifying certain anionic oligomeric esters to act more effectively as soil release agents in granular laundry detergent formulae, as distinct from industrial finishes and liquid, gel, paste-form, or dryer-added substrate types of laundry detergent formulae.
Such preoccupations take into consideration that the consumer of laundry detergents, indeed the public at large, still uses large quantities of anionic surfactant-containing granular laundry detergents (despite the growing use of liquids) and is continually demanding improvements in their formulation, environmental compatibility, cleaning, soil release effectiveness and convenience (especially compactness of form) without desiring to see embodied in the cost of granular laundry detergent products too high a cost of improvement.